Guide bar, chain incorporating such a bar and engine equipped with such a chain

ABSTRACT

This invention relates to a guide bar for a drive chain, provided with two orifices for passage of a pintle pin, each orifice being substantially triangular in shape, with substantially identical edges, in the form of arc of circle and concave. The bar is provided with a recess which extends, from an outer edge of the bar, in the direction of an opposite edge, between the afore-mentioned orifices. The bar comprises, on either side of the recess, two series of two convex edges in the form of an arc of circle, each of these convex edges being centred on the geometrical centre of one of the concave edges of a triangular orifice.

FIELD OF THE INVENTION

[0001] The present invention relates to a guide bar, to a chaincomprising such a bar, and to an engine equipped with such a chain.

BACKGROUND OF THE INVENTION

[0002] A drive chain may be used for the transmission of a movement and,in particular, for the synchronization of the elements constituting atiming system in an internal combustion engine of an automobile vehicle.

[0003] It is known from EP-A-1 072 816 to provide, in a drive chainguide bar, a recess which extends from an outer edge of the bar in thedirection of the opposite edge, between orifices for passage of pins forarticulation of this bar with other, so-called inner bars, used forconstituting the links of the chain.

[0004] The known outer, or guide bar of EP-1 072 816 functionscorrectly, but is relatively heavy, which has a negative influence onits inertia and on the dynamic behaviour of a chain comprising a largenumber of such bars. In addition, the tools for manufacturing such anouter bar must be produced by a plurality of machining operations,involving the corresponding manipulations. This results in risks oferror during the machining and control operations.

[0005] It is a more particular object of the present invention toovercome these drawbacks by proposing a guide bar for a drive chain ofthe afore-mentioned type, whose sequence of manufacture may beoptimalized, while it presents excellent mechanical properties and aninertia compatible with relatively great accelerations, for example atthe level of a sprocket of a timing system in an engine.

SUMMARY OF THE INVENTION

[0006] To that end, the invention relates to a guide bar for a drivechain, this bar being provided with two orifices for passage of a pintlepin, each orifice being substantially triangular in shape, withsubstantially identical edges, in the form of an arc of circle andconcave, this bar being provided with a recess which extends from anouter edge of the bar, in the direction of an opposite edge, betweenthese orifices. This bar is characterized in that it comprises, oneither side of the afore-mentioned recess, two series of two convexedges in the form of arc of circle, each of these convex edges beingcentred on the geometrical centre of a concave edge of a triangularorifice for passage of a pintle pin.

[0007] Thanks to the invention, the same geometrical centre is used fordefining one of the concave edges of an orifice for passage of a pintlepin and one of the convex edges of the bar in the vicinity of thisorifice, which makes it possible to produce tools for cutting out theseedges by machining, without having to displace the blank of the toolduring manufacture. In the same way, the operations of dimensionalcontrol of these tools and of these edges may be effected by taking thesame point of reference.

[0008] According to advantageous but non-obligatory aspects of theinvention, this bar incorporates one or more of the followingcharacteristics:

[0009] The bar forms, between one of its convex edges and the concaveedge of the adjacent orifice centred on the same geometrical centre, aband in the form of a section of ring, centred on the same geometricalaxis and of substantially constant width. This band makes it possibleeffectively to withstand the mechanical stresses undergone by the bar,particularly when the pintle pin is fitted and then shrunk in theorifice of substantially triangular section.

[0010] Depending on the case, the common geometrical centre may belocated in the vicinity of the outer edge of the bar or between thetriangular orifice and a median axis of the bar, located half-waybetween the two triangular-section orifices.

[0011] The radii of curvature of the convex edges of the bar arranged onthe same side of the recess are substantially equal.

[0012] A transition edge is provided, arranged between two convex edgesformed on the same side of the recess, this transition edge likewisebeing circular and convex and having a smaller radius of curvature thanthe respective radii of curvature of the two convex edges between whichit is arranged.

[0013] A transition edge is provided, arranged between one of the convexedges of the bar and the edge of the afore-mentioned recess, thistransition edge likewise being circular and convex and having a smallerradius of curvature than that of the afore-mentioned convex edge.

[0014] The afore-mentioned transition edge is tangential to the edgesbetween which it is arranged. In addition, the radius of curvature ofthe transition edges may be provided to have a value equal to e+0.365mm, where e is the thickness of the bar.

[0015] The invention also relates to a chain which comprises at leastone outer, or guiding, bar as described hereinabove. Such a chain may beused under severe conditions, while it is relatively easy tomanufacture, with satisfactory tolerances, and the mechanical stressesdue to the shrinking of the pins fitted in the triangular-sectionorifices are distributed substantially uniformly in the materialconstituting these outer bars.

[0016] Finally, the invention relates to an engine, particularly aninternal combustion engine, equipped with a chain as describedhereinabove. Such an engine functions under optimalized conditions oftransmission of the efforts of traction of the chain.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention will be more readily understood on reading thefollowing description of an embodiment of a chain in accordance with itsprinciple, given solely by way of example, and with reference to theaccompanying drawings, in which:

[0018]FIG. 1 schematically shows a portion of a chain according to theinvention, in an exploded perspective view.

[0019]FIG. 2 is a front view, on a larger scale, of a guide bar used inthe chain of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT

[0020] Referring now to the drawings, the chain 1 shown in FIG. 1 isintended to be used in an internal combustion engine of an automobilevehicle. It is formed by bars 2 and pins 3 adapted to be assembledtogether. More precisely, the bars 2 are distributed into guiding, orouter bars 20 and into intermediate, or inner bars 120. The pins 3 maybe long pins 30, intended to cooperate with bars 20 and 120, or shortpins 130 intended to cooperate solely with bars 120.

[0021] The guide bars 20 are each provided with two orifices 21 and 22for passage of a pin 30. The bars 120 are each provided with twoorifices 121 and 122 in which both a pin 30 and a pin 130 can bereceived at the same time.

[0022] Geometrical axes X₁ and X₂ represent the position of thegeometrical axis of a pin 30 received in orifices 21 or 22 when thechain is in mounted configuration. Geometrical axes X₃ and X₄ representthe position of the geometrical axis of pins 130 received in theorifices 121 and 122 of the bars 120 when the chain is in mountedconfiguration.

[0023] Otherwise, the chain 1, which extends in a directionperpendicular to axes X₁ to X₄, functions as described in EP-A-1 072816.

[0024] The bar 20 shown in FIG. 2 is made from a sheet metal plate. Itmight also be made by stacking elementary bars all having substantiallythe same thickness, these elementary bars in that case being made ofsheet metal and being pre-treated, for example hardened, in order toimprove their resistance.

[0025] Each orifice 21 or 22 is substantially triangular in shape. Theorifice 21 is thus defined by three edges B ₁, B₂ and B₃ in the form ofarc of circle and whose concavity faces the inside of the orifice 21.C₁, C₂ and C₃ respectively denote the geometrical centres of edges B₁,B₂ and B₃.

[0026] The radii of curvature R₁, R₂ and R₃ of edges B₁, B₂ and B₃ havethe same value.

[0027] Rounded connection zones Z₁, Z₂ and Z₃ are respectively providedbetween the edges B₁, B₂ and B₃, with smaller radii of curvature thanradii R₁ to R₃.

[0028]23 denotes the edge of the bar 20 intended to be oriented towardsthe centres of curvature of the trajectory of the chain 1. In otherwords, the edge 23 constitutes the inner edge of the bar 20 orientedtowards the centre of the sprockets with which the chain 1 cooperates.This edge is curved and its concavity is oriented in the direction oforifices 21 and 22.

[0029]24 denotes the outer edge of the bar 20, i.e. its edge oppositeedge 23. The edge 24 is intended to be oriented opposite the centres ofcurvature of the trajectory of the chain 1.

[0030] X-X′ denotes a median axis of the bar 20. Y-Y′ denotes an axisperpendicular to axis X-X′ and passing through the centres of theorifices 21 and 22. 241 and 242 respectively denote those parts of theedge 24 most remote from the axis Y-Y′, these parts being respectivelyarranged at the level of the orifices 21 and 22. L denotes an imaginaryline joining parts 241 and 242.

[0031] A recess E is formed at the level of edge 24, in that the edge 24is concave and located on the same side of line L, on either side ofaxis X-X′. The recess E makes it possible substantially to lighten thebar 20 with respect to the case of the edge 24 being substantiallyaligned with the line L, without weakening the mechanical strength ofthe bar 20. At the level of recess E, the edge 24 is symmetrical withrespect to axis X-X′.

[0032] B₄ denotes the edge of the bar 20 beyond part 241 with respect toaxis X-X′.

[0033] B₅ denotes the edge of the bar 20 below the orifice 21 in FIG. 2.

[0034] The edge B₄ is in the form of an arc of circle centred on pointC₁. R₄ denotes the radius of edge B₄.

[0035] As for edge B₅, it is in the form of an arc of circle centred onpoint C₂. R₅ denotes its radius.

[0036] Radii R₄ and R₅ have the same value.

[0037] As the edges B₄ and B₅ are centred on the geometrical point C₁,they may be obtained by cutting out a blank by means of tools of thepunch and die type of which the corresponding edges are obtained bymachining virtually at the same time, without manipulation ordisplacement of the punch or of the die during manufacture, whichimproves precision of manufacture and of the subsequent control. In thesame way, as the edges B₂ and B₅ are centred on the same point C₂, theymay be produced by other parts of the die and punch obtained withoutexcessive manipulation, hence a reduction in the risks of error in theoperations of machining of these tools and of control.

[0038] A transition edge B₆ is arranged between the edges B₄ and B₅ andwith a radius of curvature R₆ whose length is equal to the thickness eof the rod 20 increased by 0.365 mm. The edge B₆ is tangential to theedges B₄ and B₅.

[0039] In the same way, a transition edge B₇ is arranged between theedge B₄ and the part 243 of the edge 24 constituting the limit of therecess E. The transition edge B₇ which is circular like the edge B₆, hasa radius of curvature R₇ whose length is equal to that of the radius R₆.The edge B₇ is tangential to the edge B₄ and to part 243 of the edge 24.

[0040] Taking the foregoing into account, there is defined between theedges B₁ and B₄ a zone Z₄ in the form of a sector of ring centred onpoint C₁. In the same way, there is defined between the edges B₂ and B₅a zone Z₅, likewise in the form of a sector of ring, but centred onpoint C₂.

[0041] L₄ and L₅ respectively denote the width of the zones Z₄ and Z₅.The widths L₄ and L₅ are equal and, in practice, their value is chosenas a function of the thickness e of the bar 20.

[0042] Thanks to the characteristics mentioned above, the mechanicalstresses around the orifice 21 can be uniformly distributed, suchstresses resulting from the shrinking of a pin 30 in this orifice. Infact, it is essential that these stresses be efficiently distributed inorder to avoid an offset of the orifice 21 along the axis X-X′ orperpendicularly thereto, which might have an influence on the real pitchof the links of the chain 1. In addition, a good distribution of theefforts due to the shrinking makes it possible to avoid incipientruptures at the level of the zones of connection Z₁, Z₂ and Z₃ betweenthe edges of the orifice 21.

[0043] The geometry of the bar 20 at the level of and around the orifice22 is symmetrical to that described hereinabove with reference to theorifice 21, which enables the same advantages to be obtained.

[0044] B′₁ to B′₃ denote the edges of the orifice 22, C₁ to C₃ theirgeometrical centres and R′₁ to R′₃ their radii. B′₄ and B′₅ denote theconvex edges in arc of circle form of the bar 20 around the orifice 22.These edges B′₄ and B′₅ are respectively centred on the points C′₁ andC′₂.

[0045] R′₄ and R′₅ denote the radii of the edges B′₄ and B′₅. Transitionedges B′₆ and B′₇ are respectively defined between the edges B′₄ andB′₅, on the one hand, and between the edge B′₄ and the part 243 of theedge 24. Two zones Z′₄ and Z′₅ are defined between the edges B′₁ andB′₄, on the one hand, B′₂ and B′₅ on the other hand, with the samecharacteristics as the zones Z₄ and Z₅.

[0046] The invention therefore makes it possible to optimalize themechanical properties of the bar 20, while its mass and its inertia arereduced to a maximum.

What is claimed is:
 1. Guide bar for a drive chain, said bar beingprovided with two orifices for passage of a pintle pin, each orificebeing substantially triangular in shape, with substantially identicaledges, in the form of an arc of circle and concave, said bar beingprovided with a recess which extends from an outer edge of said bar, inthe direction of an opposite edge, between said orifices, wherein saidbar comprises, on either side of said recess, two series of two convexedges in the form of arc of circle, each of said convex edges beingcentred on the geometrical centre of a concave edge of a triangularorifice.
 2. The bar of claim 1, wherein said bar forms, between one ofits convex edges and the concave edge of the adjacent orifice centred onthe same geometrical centre, a band in the form of a sector of ring,centred on said geometrical centre and of substantially constant width.3. The bar of claim 1, wherein said geometrical centre lies in thevicinity of said outer edge of said bar.
 4. The bar of claim 1, whereinsaid geometrical centre lies between said triangular orifice and amedian axis (X-X′) of said bar.
 5. The bar of claim 1, wherein the radiiof curvature of said two convex edges arranged on the same side of saidrecess, are substantially equal.
 6. The bar of claim 1, wherein itcomprises a transition edge arranged between two convex edges formed onthe same side of said recess, said transition edge likewise beingcircular and convex and having a smaller radius of curvature than therespective radii of curvature of the two convex edges between which itis arranged.
 7. The bar of claim 1, wherein it comprises a transitionedge arranged between one of said convex edges of said bar and the edgeof said recess, said transition edge likewise being circular and convexand having a smaller radius of curvature than that of said convex edgeof said bar.
 8. The bar of claim 6, wherein said transition edge istangential to the edges between which it is arranged.
 9. The bar ofclaim 6, wherein the radii of curvature of said transition edges have avalue equal to e+0.365 mm, where e is the thickness of said bar. 10.Chain incorporating bars, wherein it comprises at least one guide baraccording to claim
 1. 11. Engine, particularly an internal combustionengine, for automobile vehicle, equipped with a chain according to claim10.